In the 4th Generation (4G) communication system, that is the next generation communication system, intensive research is being conducted to provide users with services having various Qualities of Service (QoSs) using a data rate of about 100 Mbps. In particular, in the 4G communication system, study is now made to support high-speed services in the way of guaranteeing mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system. Also, the typical 4G communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
The IEEE 802.16 communication system is a communication system applying Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to support a broadband transmission network for a physical channel of the wireless communication system. Active research has been conducted to guarantee the mobility of an MS and the flexibility of wireless networking in the IEEE 802.16 communication system and provide service more efficiently under a wireless environment experiencing great changes in traffic distribution or required calls. As one method among them, a communication system applying a multi-hop relay data forward scheme using an RS is taken into consideration.
A use of the RS in the broadband wireless communication system results in effects of an increase of coverage of a BS, throughput improvement, etc. That is, the broadband wireless communication system can improve a throughput by locating an RS in a specific area having poor channel environment. Also, the broadband wireless communication system can provide a service to enable communication between an MS out of the coverage of a BS and the BS by locating an RS near a cell boundary.
As shown in FIG. 1A, in a general relay system, a channel resource for signal transmission from a BS to an RS is separated from a channel resource for signal transmission from the RS to an MS. For example, if a channel resource is separated in time, transmission from an RS to an MS is performed after transmission from a BS to the RS is performed. FIG. 1A shows a Half Duplex Relay (HDR) wherein resources are separated in time axis. In FIG. 1A, one square means one channel, a solid line square represents a transmission duration, and a dotted line square represents a reception duration. In view of an RS, HDR divides a channel resource for use and thus the frequency efficiency of the whole system is low. Unlike HDR, Full Duplex Relay (FDR) uses the same channel resource for each transmission between a BS and an RS and between the RS and an MS and, thus, the frequency efficiency is higher than HDR.
Referring to FIG. 1B, FDR has a great possibility to cause interference in communication of an MS compared to an HDR system. In the HDR of FIG. 1A, frequency efficiency is low but, because only an RS or a BS transmits a signal for the same channel resource during a relay process, an MS does not have to consider interference from the RS. However, if adopting FDR to overcome a decrease of frequency efficiency, a transmit signal between a BS and an RS occupies the same channel resource as in FIG. 1B. The influence of interference occurring due to the BS and the RS using the same channel resource is different depending on relative positions of a BS 201, an RS 203, and MSs 205 to 207 as shown in FIG. 2. In FIG. 2, the MSs 205 and 207 are in connection to the RS 203. With respect to the MS B 207, located out of cell coverage of the BS 201, interference from the BS 201 does not matter. However, in the case of the MS A 205, if a received signal ratio of the MS A 205 from the BS 201 and the RS 203 increases more than any level depending on a relative position, etc., interference occurs and, thus, a quality of relay communication is deteriorated.
As described above, there is a problem that, when applying HDR, a transmit signal of a BS and a transmit signal of an RS occupy the same channel resource, thus causing interference.